1. Field of the Invention
The present invention generally relates to pulse tube refrigerators and regenerative refrigerators. More specifically, the present invention relates to a pulse tube refrigerator and a regenerative refrigerator each having a filter configured to remove wear dust.
2. Description of the Related Art
In recent years, cryogenic refrigerators have been used for cooling superconducting magnets at cryogenic temperatures in systems having the superconducting magnets such as a MRI (magnetic resonance imaging) apparatus. For example, a GM (Gifford-McMahon) cryogenic refrigerator, a pulse tube refrigerator, or the like has been used as the cryogenic refrigerator. These are regenerative refrigerators wherein adiabatic expansion of coolant gas is performed and cooling generated at the adiabatic expansion is stored in the regenerator material so that refrigeration and cooling are performed.
The regenerative refrigerator includes an expander and a compressor. The expander has a regenerator configured to store the cooling generated at the time of the adiabatic expansion of the coolant gas. The compressor is configured to receive the coolant gas from the expander, compress the received coolant gas, and resupply the compressed coolant gas to the expander.
The compressor has pipes at a suction side and a supply side. The pipe at the suction side is configured to suction the received coolant gas. The pipe at the supply side is configured to supply the received and compressed coolant gas. The regenerator is in mutual communication with or is blocked off from communication with the supply side of the compressor.
A rotary valve is used to connected the generator in communication with the supply side supply side of the compressor. The rotary valve is periodically switched to open and block communication with the two pipes. The rotary valve includes a disk and a sealing member. The disk is rotatable and has a communicating hole for periodically switching a communicating state and a blocking state. The sealing member is fixed so as to receive the disk while the disk is slid.
On the other hand, due to sliding of the disk and the sealing member, the sealing member is worn so that wear dust is generated. Accordingly, if the pulse tube refrigerator is operated for a long time, the wear dust flows into the regenerator so that regenerator material becomes dirty and its capacity to be cooled is degraded. In this case, the regenerator material has to be exchanged. In addition, if the wear dust flows in the compressor, the compressing capacity of the compressor is degraded.
Accordingly, it is necessary to remove the wear dust generated by the rotary valve. A method for providing a filter between the rotary valve and the regenerator in order to remove the wear dust has been suggested. For example, Japanese Laid-Open Patent Application Publication No. 2001-241793 describes an example of a pulse tube refrigerator where filters are provided between the rotary valve and the regenerator and between the rotary valve and the pulse tube.
However, when the pulse tube refrigerator having the filters configured to remove the wear dust is operated, problems discussed below arise.
In the pulse tube refrigerator described in Japanese Laid-Open Patent Application Publication No. 2001-241793, while partition members are provided between the filter and the regenerator and between the filter and the pulse tube, it is not possible to easily separate the filter and the regenerator and the filter and the pulse tube while air tightness is secured. Accordingly, it takes a long time to perform a maintenance operation including a separation operation and an exchanging operation of a filter.
More specifically, the temperature of the entirety of the pulse tube refrigerator including the regenerator and the pulse tube should be increased to normal room temperature before the separation; the pulse tube refrigerator should be disassembled so that the filter is separated from the pulse tube refrigerator; a maintenance operation such as exchange of the separated filter should be applied; the filter where the maintenance operation is completed should be connected so that the pulse tube refrigerator is reassembled; and the insides of the regenerator and the pulse tube where air is mixed and pipes for connecting the regenerator and the pulse tube should be refilled with coolant gas such as helium gas.
In addition, in the pulse tube refrigerator described in Japanese Laid-Open Patent Application Publication No. 2001-241793, partition parts are not provided at the compressor side of the filter. Accordingly, it is not possible to easily separate the filter and the compressor while air tightness is secured. Hence, it takes time to perform the maintenance operation including the separation operation and the exchange operation of the filter.
More specifically, before separation is made between the filter and the compressor, the compressor should be separated, the filter should be exchanged, and the filter should be connected to the compressor. After that, the insides of the pipes at the supply side and the suction side of the compressor where the air is mixed should be refilled with the coolant gas such as helium gas.
In addition, even if the above-mentioned maintenance operation can be easily performed, the pulse tube refrigerator should be installed in the MRI apparatus. Accordingly, it is necessary to miniaturize the entirety of the pulse tube refrigerator including the valve unit and the expander.